There is a need for an antenna that does not require a matching network within the device to which it is attached. For example, it is often desirable for the matching network of a half wave antenna to be external to the circuit board of the transmitter/receiver to which the antenna is connected. To this end, sleeve antennas are sometimes used in the prior art. Such sleeve antennas are center fed, generally avoiding the need for a matching network. However, one of the problems with the center fed sleeve antenna, is that the feed coaxial cable is "hot" and there is a slight mismatch to start with because the feed line is 50 ohms while the antenna is 70 ohms. Another problem of the sleeve antenna is that its major diameter of the sleeve is larger than what is often desirable. It is preferable to have a smaller diameter antenna, particularly when used with the relatively small transmitter/receivers in use today.
Therefore, it is desirable to provide an antenna that has a relatively small diameter. It is also desirable to provide an antenna that is well matched to the feed line. It is also desirable to provide an antenna that does not require a matching network within the internal circuitry of the transmitter/receiver.
I have discovered an antenna that is particularly useful in the cordless antenna range and the cellular antenna range, generally between about 800 MHz to 1000 MHz. Although no limitation is intended, the antenna of my invention is useful with respect to a convertible cordless/cellular phone of the type in which the transmitter/receiver is used as a cordless phone when it is within the range of the base station and is used as a cellular phone when it is out of range of the base station. The antenna of my invention has particular utility as a result of its rotatability, whereby the radiator can rotate about an axis that is generally perpendicular to the radiator.
It is an object of the present invention to provide an antenna that has a relatively small diameter.
It is another object of the present invention to provide an antenna that is well matched to the feed line.
A further object of the present invention is to provide an antenna that does not require a matching network within the internal circuitry of the transmitter/receiver.
A still further object of the present invention is to provide an antenna in which the radiator is rotatable about an axis that is generally perpendicular to the radiator.
A still further object of the present invention is to provide an antenna that is useful in the cordless telephone and cellular telephone bandwidth.
Other objects and advantages of the present invention will become apparent as the description proceeds.